This invention relates to the recording and/or reproduction of pulse encoded information and, more particularly, to control apparatus for use in a recording/reproducing system which utilizes a video signal recorder/reproducer.
A magnetic video recorder, such as a video tape recorder (VTR) exhibits a sufficiently wide recording bandwidth such that it can be used to record audio signals with extremely high fidelity. A conventional type of VTR, when used to record an NTSC color video signal, records such a signal in parallel slant tracks, each track having a video field recorded therein. In view of the relatively low frequencies of an audio signal, there is a far greater signal storage capacity in each slant track than is needed for the audio signal. Accordingly, it is not advantageous to record an analog audio signal in place of a video signal in the slant tracks of a VTR.
If an audio signal is encoded into a digital signal, such as a PCM data signal, the resultant pulse signals can be processed without a concomittent loss in signal information. That is, the pulse signals can be transmitted or recorded with great accuracy. However, in order to exhibit the necessary high bandwidth for magnetically recording such pulse signals, suitable magnetic recording equipment heretofore has been very expensive. A VTR of the type now available for home video recording use is far less expensive than professional-type high bandwidth magnetic recording equipment, yet such a VTR offers a satisfactory bandwidth characteristic to permit the magnetic recording of a pulse encoded audio signal.
In order to use a VTR advantageously for recording pulse encoded data in general, or pulse encoded audio information in particular, it is necessary to record control signals which represent, or are similar to, the normal horizontal and vertical synchronizing signals which are included in video signals. This is because the control mechanism of the VTR relies upon these synchronizing signals for the purpose of controlling the movement (e.g., rotation) of the recording/playback head or heads as well as the movement of the recording tape in close synchronism. Accordingly, simultated horizontal and vertical synchronizing signals should be generated and combined with the pulse data so as to supply the VTR with a continuous composite signal for recording which, in some important aspects, is analogous to the video signals normally recorded by such VTR. Furthermore, these simulated synchronizing signals should not interfere with the pulse data. That is, to avoid loss of useful pulse data information, such pulse data should not be replaced by the simulated synchronizing signals.
In accordance with one feature of the apparatus described below, the time domain of the pulse data is compressed for recording, thus leaving "gaps" in the pulse signal into which the desired simulated synchronizing signals can be inserted. During playback, the synchronizing signals are removed and the "gaps" are eliminated by expanding the time domain of the pulse data. This time-compression and time-expansion are achieved by using a memory device having addressable storage locations into which the pulse data is written at one rate and out of which the stored pulse data is read at a second rate. Time-compression is achieved if the second rate exceeds the first rate; and time-expansion is achieved if the converse is true.
As will be described, the memory device advantageously can be constructed to have limited storage capacity. The write-in and read-out operations, although performed at different rates, are carried out substantially independently of each other and at the same time. When pulse data is read out of the memory at a faster rate than that in which the pulse data is written in, there is the possibility that previously read data will be re-read because the faster read-out operation will have overtaken the write-in operation. If the read-out operation is permitted to continue under these circumstances, erroneous data will be read out.
During a reproducing operation the reproduced pulse data is written into the memory at a faster rate than that in which the pulse data is read out. In that event, there is the possibility that all of the storage locations in the memory will be filled because the write-in operation will have overtaken the read-out operation. Under these circumstances, the writing in of additional data will distort the data which has yet to be read out.